* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

nav {
    width: 100%;
    height: 50px;
    background-color: #333333;
}

body>div {
    width: 100%;
}

footer {
    width: 100%;
    height: 50px;
    position: absolute;
    bottom: 0px;
    background-color: #333333;
}

.center{
    width: 900px;
    margin-left: auto;
    margin-right: auto;
}